New approaches are needed to improve the treatment options of over 50 million people in the United States suffering from chronic pain. The proposed research is designed to develop a novel class of opioid analgesics that produce less tolerance and may potentially reduce opiate-associated side effects. Opioid ligands activate G protein coupled receptors (GPCR) to mediate diverse physiological functions. The regulation of these receptors can ultimately determine the extent of opioid receptor ligand efficacy. Genetically modified mice that lack molecular components of GPCR regulation display greatly attenuated opioid analgesic tolerance. Therefore, opioid agonists conferring non-conventional receptor conformations could yield novel analgesics with reduced tolerance liabilities. Recently, Herkinorin, a salvinorin A derivative, was found to be a potent and selective mu opioid receptor (MOR) agonist in vitro and in vivo. The diterpene chemical structure represents a novel lead for the design of opiate agonists with distinct pharmacological properties. This selective mu opioid receptor agonist activates the receptor, induces antinociception in rats, yet does not induce ssarrestin2 recruitment nor induce internalization of the receptor under any condition tested - distinguishing it from all known MOR agonists. The ultimate goal of this Proposal is to develop novel analgesics with reduced analgesic tolerance and side effects. We will achieve this goal using the following Specific Aims: 1): synthesize opioid ligands derived from Herkinorin to remove esterase-degradation sites, improve solubility, and preserve or improve MOR selectivity;and 2) determine pharmacological properties of Herkinorin analogs by testing activity of G protein signaling efficacy and potency and looking for absence of ssarrestin recruitment to MOR for analogues that efficaciously and potently activate MOR-mediated G protein coupling. Mencuro Therapeutic Inc. was co-founded by the inventors of these compounds, to commercialize this technology by developing potent mu opioid receptor agonists without the usual opioid side-effects. SARmont, LLC, is a drug discovery and design company, led by Dr. John Talley, the lead inventor of Celebrex(R) and 7 other NCEs that have made it to the marketplace. Mencuro will contract SARmont to provide medicinal chemistry services, specifically in compound synthesis, molecular design, and structure- activity relationship analysis. Mencuro will conduct all the in vitro testing. Success in this Proposal will lead to the submission of a Phase II grant focused on further medicinal chemistry optimization for potency and selectivity, in vivo validation using established mammalian models for pain treatment, and pre-clinical safety studies required for IND submission. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE Chronic and persistent, severe pain results from many disorders and diseases and affects over 80 million adults annually. Opioid analgesics block pain perception by targeting the mu opioid receptor (MOR);however, this receptor also mediates unwanted opioid side-effects such as tolerance, dependence, constipation and overdose. The goal of this Proposal is to create MOR agonists that provide pain relief without unwanted side-effects.